Clinical protection, sub-clinical infection and persistence following vaccination with extinction payloads of O1 Manisa foot-and-mouth disease monovalent vaccine and challenge in goats and comparison with sheep

Abstract

Small ruminants play an important role in the epidemiology of Foot-and-Mouth Disease (FMD). Small ruminants are vaccinated with one-half or one-third of cattle dose of oil-based or aqueous vaccines respectively. The extinction antigen payload in vaccine for protection in small ruminants is poorly studied. FMD seronegative Nellore sheep (n=30) and Osmanabadi goats (n=30) were vaccinated with different payloads of O1 Manisa vaccine (0.45–5μg). Vaccinated and sero-negative unvaccinated sheep (n=6) and goats (n=6) were challenged intradermally into the coronary band with O1 Manisa virus. The sheep and goats were monitored for signs of FMD and samples were collected for measuring viraemia and virus associated with nasal swabs and probang samples. Clotted blood was collected for serology. Vaccines containing antigen payload up to 0.94μg protected sheep and goats against challenge. Sheep and goats vaccinated with 0.45μg antigen payload were poorly protected against challenge. An antigen payload of 0.94μg was sufficient to offer complete protection and also absence of carrier status. Sheep and goats with no vaccination or with poor sero conversion to vaccination showed sub-clinical infection and became carriers. The results of the study suggest that vaccination offers protection from clinical disease even at a low payload of 0.94μg and hence one-half of cattle dose of the oil-based vaccine formulations is sufficient to induce protective immune response in sheep and goats. Since no live virus could be isolated after 5days post challenge from the nasal swab or probang samples even though viral RNA was detected, the risk of these animals transmitting disease was probably very low.